Muscle cell electrical hyperpolarization and reduced exercise hyperkalemia in physically conditioned dogs.

Knöchel, James P.; Blachley, Jon D.; Johnson, John H.; Carter, Norman W.

doi:10.1172/jci111755

Cited by 79 publications

(50 citation statements)

References 40 publications

(27 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…It is conceivable that a difference of K + , if any, should be in the opposite direction than that observed, due to the larger muscular mass of obese subjects releasing K + (increased FFM, higher values of creatine kinase [27]). The results of K + could be in line with the hypothesis of an increased density of the Na + -K + pump sites in their skeletal muscles, as it has been observed in trained dogs [13]. …”

Section: Discussionsupporting

confidence: 85%

“…In obese subjects, a low respiratory exchange ratio indicated a condition of insulin resistance, which persisted during physical activity, implying a preference for lipids [11]. We hypothesized that the amounts of neutral lipids might reflect insulin resistance [12], likely affecting the production of lactate anions, and that hypertrophy might control potassium release on the basis of an increased activity of membrane ATPase that has been described in hypertrophic muscular fibers [13]. …”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Ventilation and Its Control during Incremental Exercise in Obesity

et al. 2006

View full text Add to dashboard Cite

Background: In obesity, the addition of mass loading of the chest wall by adipose tissue decreases compliance, but its ventilation does not seem to be a limiting factor to physical performance. Plasma K⁺ and lactic acid are considered important determinants of ventilation during exercise. Obesity is characterized by insulin resistance. Objectives: The aim of this study was to assess ventilatory adaptations to sustained effort and the effects of lactic acid and potassium in young obese subjects. Methods: Twelve obese subjects with a body mass index of 40 (mean age 27 years, 6 males) and 12 normal subjects with a body mass index of 22 (aged 28 years, 6 males) performed a progressive cycloergometric test with increases of 20 W every 4 min to exhaustion while minute ventilation, oxygen consumption, carbon dioxide production, end-tidal oxygen pressure, and end-tidal carbon dioxide pressure were measured. Blood samples were collected at the end of every step to determine plasma K⁺. Lactic acid was measured at rest, 40, 80, 120 W and peak exercise (or only at peak exercise if <120 W). Before each exercise, we tested insulin sensitivity using the quantitative insulin sensitivity check index. Results: Obese subjects had lower insulin sensitivity (0.318 vs. 0.345, p < 0.01). Peak exercise was not significantly different between both groups (125 W in the obese group vs. 137 W in the control group), but the ventilatory threshold was at lower power output in the obese group compared to the controls (76 vs. 107 W, p < 0.05). Ventilation increased less in the obese group but oxygen saturation of hemoglobin remained within normal limits up to exhaustion in both groups. Ventilation was appropriate for the CO₂ increase but less appropriate for the increased O₂ consumption. Both K⁺ and lactic acid increased less in the obese group. Conclusions: In our obese subjects, ventilation was not a limiting factor during exercise. Its lower increase may be due, in addition to the characteristics of their chest walls, to insulin resistance which may limit the increase in lactic acid during effort, and to the hypertrophy of muscle fibers previously noted, which may be linked to a lower increase in plasma K⁺ during physical exercise.

show abstract

Section: Discussionsupporting

confidence: 85%

Section: Introductionmentioning

confidence: 99%

Ventilation and Its Control during Incremental Exercise in Obesity

et al. 2006

View full text Add to dashboard Cite

show abstract

“…The generation of an action potential is associated with an outward flux of K ϩ , which thus determines a net loss of K ϩ from the cell (9). The increase in interstitial potassium concentration reduces the resting membrane potential and results in a reduced facilitation of propagation of the action potential (19). The loss of K ϩ is counteracted by the Na ϩ -K ϩ pump.…”

Section: Discussionmentioning

confidence: 99%

Conduction velocity of low-threshold motor units during ischemic contractions performed with surface EMG feedback

Farina¹,

Gazzoni²,

Camelia³

2005

Journal of Applied Physiology

View full text Add to dashboard Cite

Farina, Dario, Marco Gazzoni, and Federico Camelia. Conduction velocity of low-threshold motor units during ischemic contractions performed with surface EMG feedback. J Appl Physiol 98: 1487-1494, 2005. First published November 12, 2004 doi:10.1152/ japplphysiol.01032.2004.-The aim of this study was to analyze the effect of ischemia on low-threshold motor unit conduction velocity. Nine subjects were trained to isolate the activity of a single motor unit (target motor unit) in the abductor pollicis brevis muscle with feedback on surface EMG signals recorded with a 16-electrode linear array. After training, the subjects activated the target motor unit at ϳ8 pulses per second (pps) for five 3-min-long contractions. During the third and fourth contractions, a cuff inflated at 180 mmHg around the forearm induced ischemia of the hand. The exerted force (mean Ϯ SE, 4.6 Ϯ 2.1% of the maximal voluntary contraction force), discharge rate (8.6 Ϯ 0.4 pps), interpulse interval variability (34.8 Ϯ 2.5%), and peak-to-peak amplitude of the target motor unit action potentials (176.6 Ϯ 18.2 V) were not different among the five contractions. Conduction velocity, mean power spectral frequency, and action potential duration were the same in the beginning of the five contractions (2.8 Ϯ 0.2 m/s, 195.2 Ϯ 10.5 Hz, and 5.4 Ϯ 0.3 ms, respectively) and changed over the 3 min of sustained activation only during the fourth contraction. Conduction velocity and mean power spectral frequency decreased (10.05 Ϯ 1.8% and 8.50 Ϯ 2.18% during the 3 min, respectively) and action potential duration increased (8.2 Ϯ 4.6% in the 3 min) during the fourth contraction. In conclusion, 1) subjects were able to isolate the activity of a single motor unit with surface EMG visual feedback in ischemic conditions maintained for 16 min, and 2) the activation-induced decrease in single motor unit conduction velocity was significantly larger with ischemia than with normal circulation, probably due to the alteration of mechanisms of ion exchange across the fiber membrane.

show abstract

“…With dencrvation, tenotomy or immobilization by a cast rodent skeletal muscle Na,K-ATPase concentration is reduced (6,20). Physical training in mammals induces an upregulation of skeletal muscle Na,K-ATPase, followed by a downregulation during deconditioning (20,26). In cardiac muscle a similar relationship is seen (20).…”

Section: Introductionmentioning

confidence: 93%

Quantification of the total Na,K-ATPase concentration in atria and ventricles from mammalian species by measuring3H-ouabain binding to intact myocardial samples. Stability to short term ischemia reperfusion

et al. 1990

View full text Add to dashboard Cite

Na,K-ATPase concentration was measured by vanadate facilitated 3H-ouabain binding to intact samples taken from various parts of porcine and canine myocardium. In porcine and canine heart 3H-ouabain binding site concentration in ventricles was 1.4-2.5 times larger than in atria. Evaluation of 3H-ouabain binding kinetics revealed no major difference between atria and ventricles: Equilibrium was obtained after the same incubation time in right atrium (RA) as in left ventricle (LV), both in porcine and canine heart. Unspecific uptake and retention of 3H-ouabain was for porcine heart RA and LV 1.5 and 1.4, respectively, and for canine heart RA and LV, both 1.2% filling (i.e., volume (ml) of incubation medium 3H-radioactivity taken up per mass unit (g wet wt.) of tissue multiplied by 100). The apparent dissociation constant (KD) was 1.4 x 10(-8) and 1.9 x 10(-8) in porcine RA and LV and 2.6 x 10(-8) and 6.1 x 10(-8) mol/l in canine RA and LV. Loss of specifically bound 3H-ouabain during the washout procedure occurred with a half-life time (T1/2) of 16.7 and 28.6 in RA and LV of porcine heart and 91.2 and 151.6 h in RA and LV of canine heart. Duly corrected for these errors of the method--factor 1.16 and 1.13, respectively, for porcine RA and LV, and factor 1.11 and 1.13 for canine RA and LV, total 3H-ouabain binding site concentration was found to be 553 +/- 74 and 1037 +/- 45 pmol/g wet wt. (means +/- SEM, n = 5) in porcine RA and LV, and 569 +/- 37 and 1410 +/- 40 pmol/g wet wt. (means +/- SEM, n = 5) in the canine RA and LV. These values were confirmed by measurements of 3H-digoxin binding to the porcine heart. The present quantification of myocardial Na,K-ATPase gives values up to 154 times higher than measurements based upon Na,K-ATPase activities in membrane fractions where the recovery of Na,K-ATPase may be less than 1% due to loss during purification. A higher Na,K-ATPase concentration is found in small animals than in large animals. A relationship between higher concentration of Na,K-ATPase and larger pressure work in ventricles compared to atria is suggested. Myocardial 3H-ouabain binding sites were found to be stable for 20 min of ischemia, followed by 1 h of reperfusion, supporting the concept that myocyte injury induced by short term ischemia may be reversible and that reperfusion may result in normalization.

show abstract

Muscle cell electrical hyperpolarization and reduced exercise hyperkalemia in physically conditioned dogs.

Cited by 79 publications

References 40 publications

Ventilation and Its Control during Incremental Exercise in Obesity

Ventilation and Its Control during Incremental Exercise in Obesity

Conduction velocity of low-threshold motor units during ischemic contractions performed with surface EMG feedback

Quantification of the total Na,K-ATPase concentration in atria and ventricles from mammalian species by measuring3H-ouabain binding to intact myocardial samples. Stability to short term ischemia reperfusion

Contact Info

Product

Resources

About